The present invention relates to an improved structure of joystick switch assembly which has convex portions on two opposite sides of the contact plate of the joystick thereof, wherein when the joystick is moved the convex portions are forced to squeeze a respective conductive rubber to vary a set of impedances defined across respective impedance points on a respective membrane circuit thereby indicating the amount and direction of the movement of the joystick.
A variety of computers are known and widely used in different fields, For full screen editing, a computer system is generally equipped with a joystick for controlling a movement of the cursor on the screen. FIG. 1 shows a joystick switch assembly according to the prior art which is generally comprised of a rubber cap 11, a joystick 12, a cover shell 13, a conductive rubber 14, and a circuit board 15. The joystick 12 comprises a joystick body 121 extending out of the cover shell 13 through a center through-hole 131 in the cover shell 13, and a flat contact plate 122 received within a storage chamber 132 defined within the cover shell 13. The rubber cap 11 covers the top of the joystick body 121. The circuit board 15 is fastened to connecting portions 133 at the bottom of the cover shell 13 by a welding process, and has a plurality of impedance points. The conductive rubber 14 is disposed between the circuit board 15 and the flat contact plate 122 of the joystick 12. When the joystick 12 is moved, the flat contact plate 122 is forced to squeeze the conductive rubber 14 causing variations in the impedance across the respective impedance points on the circuit board. The variations can be used to produce a signal output which is produced proportional to the amount and direction of the movement of the joystick and sent to the mainframe of the computer system to change the position of the cursor on the screen. However, this structure of joystick has drawbacks. Because the contact plate 122 of the joystick 12 is a flat plate, an error contact between the contact plate 122 and the impedance points on the circuit board 15 tends to happen. Therefore, the sensitivity of this structure of joystick is low. Another drawback of this structure of joystick is that the conductive rubber 14 will wear off quickly because of its broad contact area between the contact plate 122 of the joystick 12 and the circuit board 15. Still another drawback associated with this joystick structure is its low sensitivity and low accuracy because there is only one circuit board disposed at one side by the contact plate 122 of the joystick 12 for creating the impedance.